A projection type video display such as a liquid crystal projector has a display such as a liquid crystal panel adapted to modulate light emitted from a lamp, e.g. an ultra-high pressure mercury lamp serving as a light source, based on a video signal, and cast the modulated light to display a video associated with the video signal. This type of display is equipped with lamp cooling means for cooling the lamp.
In such a conventional projection type video display as mentioned above, the lamp cooling means is enabled immediately after power is applied to the lamp, thereby starting cooling (ordinary cooling) of the lamp immediately after the lamp is turned on or started up based on a presumed stationary operating condition of the lamp at high temperature.
There is disclosed in Japanese Patent Application Laid Open No. 24-348109 (G03B 21/16) a technique of determining the necessity of cooling of a lamp based on the lamp temperature and executing cooling if needed. This prior art projection type display, adapted to cast light to project a video by modulating the light emitted from a lamp, comprises: cooling means for cooling the lamp; time management means for managing time that elapses after said lamp is turned off; and control means for controllably turning on the lamp based on the output of the time management means after the lamp is sufficiently cooled by the cooling means if the temperature of the lamp to be turned on is higher than a predetermined temperature, but turning on the lamp without cooled it if its temperature is lower than the predetermined temperature. In other words, as is apparent from the preceding description and paragraphs 14, 39-43, 47-50, and FIGS. 5 and 7 of the cited reference, the prior art performs cooling of the lamp before the lamp is turned on if its temperature is high but otherwise performs cooling simultaneously with the turn-on of the lamp.
Thus, in the prior art, ordinary cooling of the lamp is always performed from the beginning of a startup operation of the lamp, which disadvantageously delays evaporation of mercury in the lamp, particularly when the lamp temperature is low, hence delaying the development of the startup process of the lamp.